The present invention relates particularly to electrolytic removal (e.g., dissolution, etching, or polishing) methods for use in the formation of various structures on substrates, such as semiconductor substrates or substrate assemblies.
Films of metals and metal oxides, particularly the heavier elements of Groups 8-11 (Fe, Co, Ni, and Cu groups), are becoming important for a variety of electronic applications. This is at least because many of the Group 8-11 metal films (e.g., Pd, Pt) are generally unreactive, resistant to oxidation or retard the diffusion of oxygen, and are good conductors. Oxides of certain of these metals also possess many of these properties, although perhaps to a different extent.
Thus, films of Group 8-11 metals, their alloys, and metal oxides, particularly the second and third row metals (e.g., Ru, Os, Rh, Ir, Pd, and Pt) have suitable properties for a variety of uses in integrated circuits. For example, they can be used in integrated circuits for barrier materials, for example. They are particularly suitable for use as barrier layers between the dielectric material and the silicon substrate in memory devices. Furthermore, they are suitable as the plate (i.e., electrode) itself in capacitors.
Platinum is one of the candidates for use as an electrode for high dielectric capacitors. Capacitors are the basic charge storage devices in random access memory devices, such as dynamic random access memory (DRAM) devices, static random access memory (SRAM) devices, and now ferroelectric memory (FE RAM) devices. They consist of two conductors, such as parallel metal or polysilicon plates, which act as the electrodes (i.e., the storage node electrode and the cell plate capacitor electrode), insulated from each other by a dielectric material (a ferroelectric dielectric material for FE RAMs). Thus, there is a continuing need for methods for the processing, e.g., removal, of Group 8-11 metal-containing films, preferably, platinum-containing films.
The planarization of a surface that includes platinum and other Group 8-11 metals typically involves mechanical polishing, as opposed to chemical-mechanical polishing, because they are relatively chemically inert and/or have relatively few water soluble products. Such mechanical polishing uses alumina, silica, or other abrasive particles to remove the metal physically. Unfortunately, mechanical polishing tends to smear (e.g., deform) the metals, leaving metal over undesired portions of the wafer surface, and leaving scratches in either the metal itself or other areas on the wafer surface. Also, many commercially available abrasive slurries do not effectively planarize platinum or other Group 8-11 metal-containing surfaces either because no material is removed or the resultant surface has defects therein.
Various etching processes are used in the fabrication of semiconductor devices to remove various materials. Such etching processes are used to control and maintain critical dimensions of various device structures such as, for example, transistors, capacitors, and interconnects. However, the removal of materials such as Group 8-11 metal-containing films by wet etching, for example, is generally very difficult. This is particularly true with respect to films containing rhodium, iridium, alloys thereof, and oxides thereof. For example, removal of metallic rhodium (Rh) and iridium (Ir) requires the use of high temperatures and/or high pressures with strong oxidizers and acids.
Thus, a need still exists for methods of removal of materials, particularly Group 8-11 metal-containing films, from semiconductor substrates or substrate assemblies.
The present invention provides methods that overcome many of the problems associated with the removal of platinum and/or other of the Group VIIIB metals (i.e., Groups 8, 9, and 10 of the Periodic Table of Elements) and Group IB metals (i.e., Group 11 of the Periodic Table of Elements) from substrates. Preferably, the methods of the present invention are effective for the removal of at least one of the second and/or third row metals of Group VIIIB (i.e., Groups 8, 9, and 10, which include Rh, Ru, Ir, Pd, Os, and Pt) and/or Group IB (i.e., Group 11, which includes Au and Ag) from a surface. More preferably, the methods of the present invention are effective for the removal of at least one of Co, Rh, Ru, Ir, Ni, Pd, Pt, Os, Au, and Ag from a surface. Most preferably, the methods of the present invention are effective for the removal of at least one of Rh, Ir, and Pt, or alloys thereof, from a surface. Such a surface is referred to herein as a xe2x80x9cmetal-containing surface.xe2x80x9d
That is, a xe2x80x9cmetal-containing surfacexe2x80x9d refers to an exposed region having a metal present, preferably at least one metal of the Periodic Table Groups 8-11 present. In such an exposed region, the metal is preferably present in an amount of at least about 10 atomic percent, more preferably at least about 20 atomic percent, and most preferably at least about 50 atomic percent, of the composition of the region, which may be provided as a layer, film, coating, etc., to be etched in accordance with the present invention. The surface preferably includes one or more Group 8-11 metals in elemental form or an alloy thereof (with each other and/or one or more other metals of the Periodic Table), as well as conductive oxides and silicides thereof. More preferably, the surface includes (and most preferably, consists essentially of) one or more Group 8-11 metals in elemental form or an alloy of such metals only.
In one embodiment of the invention, there is a method for electrochemically removing a metal from a substrate surface with an electrolyte. The method includes: providing an electrochemical cell that includes: a reservoir for containing an electrolyte; a first electrode that includes a substrate having a metal-containing surface positioned to interface with the electrolyte; and a counter electrode in electrical contact with the first electrode; and applying an alternating or bipolar pulsed electrical current to the electrochemical cell. In one embodiment of this method, the metal-containing surface includes a metal selected from the group consisting of a Group VIIIB metal (i.e., Groups 8, 9, and 10) and a combination thereof. In another embodiment of this method, the metal-containing surface includes a metal selected from the group consisting of a Group IB metal (i.e., Group 11) and a combination thereof.
In another embodiment of the invention, there is a method for electrochemically removing a metal from a substrate surface with an electrolyte, wherein the method includes: providing an electrochemical cell that includes: a reservoir for containing an electrolyte; a first electrode that includes a substrate having a metal-containing surface positioned to interface with the electrolyte; and a counter electrode in electrical contact with the first electrode; wherein the substrate is a semiconductor substrate or substrate assembly; and applying an alternating electrical current to the electrochemical cell. In one embodiment of this method, the metal-containing surface includes a metal selected from the group consisting of a Group VIIIB metal (i.e., Groups 8, 9, and 10) and a combination thereof (preferably, a Group VIIIB second row metal (Ru, Rd, Pd), a Group VIIIB third row metal (Os, Ir, Pt), or a combination thereof). In another embodiment of this method, the metal-containing surface includes a metal selected from the group consisting of a Group IB metal (i.e., Group 11) and a combination thereof (preferably, a Group IB second row metal (Ag), a Group IB third row metal (Au), or a combination thereof).
The present invention also provides an apparatus for electrochemically removing a metal from a substrate surface with an electrolyte.
In one embodiment, the apparatus includes: a reservoir for containing an electrolyte; a first electrode that includes a substrate having a metal-containing surface positioned to interface with the electrolyte; a counter electrode in electrical contact with the first electrode; and a power supply to deliver alternating or bipolar pulsed current between the first electrode and the counter electrode. In one embodiment of this apparatus, the metal-containing surface includes a metal selected from the group consisting of a Group 8-10 metal and a combination thereof. In another embodiment of this apparatus, the metal-containing surface includes a metal selected from the group consisting of a Group 11 metal and a combination thereof.
In another embodiment, the apparatus includes: an electrolyte composition; a first electrode that includes a substrate having a metal-containing surface positioned to interface with the electrolyte composition; a conductive polishing pad for electrical contact with the first electrode; an abrasive for polishing the metal-containing surface; a carrier assembly comprising a substrate holder to support the substrate; a drive assembly for use in rotating at least one of the substrate holder and conductive polishing pad; and a power supply to deliver alternating or bipolar pulsed current between the first electrode and the counter electrode. In one embodiment of this apparatus, the metal-containing surface includes a metal selected from the group consisting of a Group 8-10 metal and a combination thereof. In another embodiment of this apparatus, the metal-containing surface includes a metal selected from the group consisting of a Group 11 metal and a combination thereof.
As used herein, xe2x80x9csemiconductor substrate or substrate assemblyxe2x80x9d refers to a semiconductor substrate such as a base semiconductor layer or a semiconductor substrate having one or more layers, structures, or regions formed thereon. A base semiconductor layer is typically the lowest layer of silicon material on a wafer or a silicon layer deposited on another material, such as silicon on sapphire. When reference is made to a substrate assembly, various process steps may have been previously used to form or define regions, junctions, various structures or features, and openings such as capacitor plates or barriers for capacitors.